"""
7-4 计算前n项的和。
"""

import math


def fact(n):
    result = 1
    for i in range(1, n+1):
        result *= i
    return result


def resolution1():
    n = int(input())
    array = []
    item = 0
    for i in range(1, n+1):
        item = ((math.pow(-1, i-1)) / (fact(2*i-1)))
        array.append(item)
    result = sum(array)
    print("%.6f" % result)


if __name__ == '__main__':
    resolution1()